1. Field of the Invention
The present invention relates to a technology of crimping a terminal onto an electric wire.
2. Description of the Related Art
When a terminal such as a connector terminal is crimped onto an end part of an electric wire, it is an important goal to increase holding force therebetween and reduce connection resistance therebetween. Note that the holding force refers to force required for separating an end part of an electric wire and a terminal when they are applied with strength in a drawing direction, and that the connection resistance refers to a resistance value between the terminal and the electric wire.
The holding force has a tendency to increase as compressibility is gradually increased and decrease when compressibility reaches or surpasses a certain point.
In addition, the connection resistance shows a tendency to keep decreasing when compressibility is gradually increased and conversely increase when compressibility reaches or surpasses a certain point.
The same compressibility is not an optimum point for both, but a point at which the largest value of holding force is exhibited and a point at which the smallest value of connection resistance have compressibilities different from each other.
FIG. 12 is a figure illustrating a relationship between crimp height and holding force or connection resistance in a case where a terminal is crimped onto an end part of an electric wire. Herein, the crimp height (mm) represents a height of a crimper with respect to an anvil when the terminal is crimped using a crimping mold, in which there is established a relationship that compressibility is higher as the crimp height becomes smaller and lower as the crimp height becomes larger.
This figure shows a change curve C1 indicating holding force (at initial stage immediately after crimping), a change curve C2 indicating connection resistance (at initial stage immediately after crimping) and a change curve C3 indicating connection resistance (after endurance test) corresponding to a plurality of crimp heights H1 to H7.
As shown in this figure, it is understood that crimping is performed excessively in a case where the crimp height is small (H1 and H2), leading to a decrease in holding force. If force in a drawing direction is applied on the end part of the electric wire and the terminal on this occasion, the end part of the electric wire tends to be broken to be separated therefrom in a crimping portion. Meanwhile, relatively strong holding force can be obtained in a case where the crimp height is relatively appropriate (from H3 to H5). If force in a drawing direction is applied on the end part of the electric wire and the terminal on this occasion, the electric wire tends to be broken to be separated therefrom in a portion other the crimping portion. Moreover, it is understood that crimping is performed loosely in a case where the crimp height is large (H6 and H7), leading to a decrease in holding force. If force in a drawing direction is applied on the end part of the electric wire and the terminal on this occasion, the end part of the electric wire tends to come out of the terminal to be separated therefrom.
Besides, it is understood from this figure that connection resistance tends to be relatively large in the case where the crimp height is small (H1 and H2), relatively small in the case where the crimp height is relatively appropriate (from H3 to H5), and relatively large in the case where the crimp height is large (H6 and H7).
Therefore, it is possible to make relatively large holding force and relatively small connection resistance compatible with each other if crimping is performed within a medium level of compressibility range (in an example of FIG. 12, within the range of crimp height H3 to H5).